GB2234359A

GB2234359A - Exposure control unit for a motor driven camera shutter

Info

Publication number: GB2234359A
Application number: GB9015084A
Authority: GB
Inventors: Kanji Ito; Mitsuhiro Kakuta
Original assignee: Seikosha KK
Current assignee: Seikosha KK
Priority date: 1989-07-10
Filing date: 1990-07-09
Publication date: 1991-01-30
Anticipated expiration: 2010-07-09
Also published as: DE4021803A1; GB2234359B; JPH0342639A; US5070354A; GB9015084D0; JP2551846B2

Description

1 EXPOSURE CONTROL UNIT FOR A MOTOR DRIVEN SHUTTER FOR A CAMERA The

present invention relates to an exposure control unit for a motor driven shutter for a camera.

A conventional motor driven camera shutter is driven in accordance with an exposure value EV, which is calculated from shutter exposure time or shutter speed TV, stop value AV, film sensitivity SV, object luminance BV and so forth. The exposure value EV is calculated by a method call APEX (the additive system of photographic exposure), in which processing can be performed in the camera by an adding operation because the shutter speed, is stop values and so forth follow a geometric series.

The exposure characteristics of the motor driven shutter are controlled by exposure data EDn corres ponding to calculated exposure values EVn. However, when the exposure data EDn is initally interpolated against the exposure values EVn in a geometric series, the quantity of exposure data EDn becomes, for example, four times as large as the number of terms in the series. Thus, there is a problem in that the exposure data EDn requires the capacity of a ROM in the exposure control unit to be increased for storage.

Further, there is another drawback in that increasing the ROM capacity produces a cost increase in a processor IC which contains the ROM, and different exposure data EDn has to be entered in advance for every type of exposure control unit according to the circumstances.

It is an object of the present invention to provide a exposure control unit for motor driven shutter for a camera, which is capable of exposure control with i 2 C) 10 is higher accuracy as compared with the exposure control unit heretofore in use without increasing the exposure data needing to be stored.

In accordance with the invention, this is achieved by providing means for interpolating on the basis of a linear approximation between adjacent exposure data values as stored.

Although the present invention is primarily directed to any novel integer or step, or combination of integers or steps, herein disclosed and/or as shown in the accompanying drawings, nevertheless, according to one particular aspect of the present invention to which, however, the invention is in no way restricted, there is provided an exposure control unit for a motor driven shutter for a camera comprising a photometric circuit arranged to receive incident light from an object and to generate an object luminance value as luminance data, a store for an exposure table, in which exposure data corresponding to said luminance data for controlling the motor driven shutter for exposure is stored, and means for performing an interpolating operation on the exposure data by interpolating between adjacent exposure values as stored as said exposure data table on the basis of a linear approximation for calculating a proper exposure value for controlling the motor driven shutter.

The exposure control unit is thus capable of finely controlling the exposure of the motor driven shutter from the exposure data.

The present invention is described further, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a block diagram showing a embodiment of a exposure control unit for a motor driven shutter for a camera according to the present invention; 11 1 i 1 1 1 1 3 Figure 2 is a diagram showing a data table stored in a ROM of the exposure control unit of Figure 1; and Figures 3 and 4 are graphs of characteristics relating to the data represented in Figure 2.

An embodiment of a exposure control unit for a motor driven shutter for a camera according to the present invention will be described in detail with reference to Figure 1 and Figure 2.

As shown in Figure 1, the exposure control unit has object luminance input means 2 and ISO information input means 3 for supplying object luminance BV, and film sensitivity SV to a control circuit 4. A ROM 5 stores exposure data EDn, where n equals 17, 16 3/4, 16 1/2..., as shown in Figure 2 in sets of four values representing a multiple series corresponding to exposure values EVn.

In the control circuit 4, processing means 4a for performing an interpolating operation on the exposure data is provided with a program logic. The processing means 4a calculate driving data EXDx on the basis of the following expression (l):

EXDX = { ED(a+d) - EDa x (x-a)} + EDa... (1) d where X designates a data value EDX corresponding to a proper exposure value EV on the basis of which the driving data EXDx is calculated, a and (a+d) designate exposure data values EDa and ED(a+d) in addresses in the ROM 5 before and after the exposure data value EDx and d represents a dividing number by which the multiple series for the exposure data EDn is split.

When a release button 1 is depressed, the driving i 4 data EXDx is calculated in the control circuit 4, and the shutter blades 6a of a shutter mechanism 6 is open and closed.

When the proper exposure value is EV occurs at X = 16 1/6 in the exposure control unit for the motor driven shutter constructed as described above, a is 16 and (a+d) is 16 1/4 in the expression (1). Therefore, the driving data EXDx is obtain from expresion (2) below:

ED(16.1) ED(16) EXDx 4 x (1616160+ ED(16)... (2) Thus, the driving data EXDx obtained from the expression (2) corresponds to the proper exposure value EV calculated on the basis of ED (16 1/4) and ED (16).

When the exposure value EVn, which is desired to be interpolated from EDa with a as 16 and ED (a+d) with (a+d) as 16 1/4 along an x-axis of a curve CA 1 of the exposure value EVn versus the exposure data EDn shown in Figure 3, is based on X as 16 1/6, the driving data EXDx calculated from the expression (2) is obtained as EXD (16 1/6).

In the above described embodiment, the multiple series has been split at equal intervals with the dividing number being 1/4. However, a finer division may be made for obtaining d 1, d 2, in the case where a rate of change is high, in accordance with a curve CA 2 as shown in Figure 4 to. enable compensation with higher accuracy to be achieved.

The exposure control unit for a motor driven 1 Z t shutter according to the present invention as described above is composed of a photometric circuit which rec. eives incident light from an object and outputs an object luminance value as luminance data, a store for an exposure table, in which exposure data corresponding to said luminance data for controlling said motor driven shutter for a proper exposure is stored, and processing means for performing an interpolation operation on the exposure data by interpolating on the basis of a linear approximation between mutual exposure data values stored in the exposure data table. The motor driven shutter may thus be driven by a motor rotating according to the interpolated exposure data. Therefore, it is possible to generate a quantity of exposure data several times as large as the exposure data that has been stored.

Accordingly, exposure control with high accuracy can be obtained without increasing the capacity of the ROM in the exposure control unit, and processor ICs which differ by unit type need not be provided.

is t 1 6

Claims

C L A I M S

1. An exposure control unit for a motor driven shutter for a camera comprising a photometric circuit arranged to receive incident light from an object and to generate an object luminance value as luminance data, a store for an exposure table, in which exposure data corresponding to said luminance data for controlling the motor driven shutter for exposure is stored, and means for performing an interpolating operation on the exposure data by interpolating between adjacent exposure values as stored as said exposure data table on the basis of a linear approximation for calculating a proper exposure value for controlling the motor driven shutter.

2. A camera including an exposure control unit as claimed in claim 1.

3. A camera as claimed in claim 2 having a motor driven shutter arranged to be driven by a rotary motor.

4. An exposure control unit of a motor driven shutter, comprising a photometric circuit which receives incident light from an object and outputs object luminance as luminance data, a motor driven shutter Which is driven by a motor rotating with exposure data corresponding to said luminance data, an exposure data table in which exposure data controlling said motor driven shutter at a proper exposure are stored, and a means of interpolating operation among exposure data which interpolates between mutual exposure data stored in said exposure data table with linear approximation.

5. A exposure control unit substantially as herein particularly described with'reference to and as illustrated in the accompanying drawings.

1.

i i 7 - 1 6. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of or relates to the same, or a different, invention from that of the preceding claims.

published 1991 at Ite Patent Office. State House. 66171 High Holbom. London WC1R47P. Further copies may be obtained from "es Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport NP1 711Z Printed by Multiplex techniques ltd. St Mary Cray, Kent.

Sales Branch. Unit b. Nine mile Point- cv=teiiniacn. t-ross neys. newpurk. jnr. -- --.Y.- ---